A power amplifier that is designed to drive inductive loads typically operates as a high-current switching device. Power amplifiers of this type are used, for example, to drive the yoke mechanism of the horizontal deflection circuitry of a display system employing a cathode ray tube (CRT). Typical prior art deflection amplifiers are described in U.S. Pat. No. No. 4,670,692, 4,642,533, 4,205,259, 3,501,672 and 3,480,826, which are incorporated herein by reference.
The switching rate or operating frequency of the deflection amplifier is one factor that determines the degree of resolution of an image formed on the CRT. As the need has increased for progressively higher resolution, so has deflection amplifier operating frequency. Deflection amplifiers operating at 64-270 kHz or higher are now much desired.
There are several reasons why it is difficult to operate CRT deflection amplifiers and other inductive load amplifiers at comparatively high frequencies. For example, (1) the effect of leakage inductance in the impedance transformer and the impedance of series inductors typically employed in such amplifiers increase with increasing frequency, making it harder to supply sufficient drive to the amplifier, and (2) prior art deflection amplifiers waste power and create dissipation and overheating problems in the amplifier and/or in the circuitry required to drive the amplifier which grow rapidly worse as frequency increases. A further problem with prior art circuits is that they do not provide independent control of the positive and negative current pulses usually employed in such amplifiers with the result that operation of the amplifier is not fully optimized.